Among the thermoplastic resin films, a biaxially stretched polyester film has been widely used as a substrate film in many applications such as magnetic recording materials and packaging materials since the film has properties excellent in mechanical properties, electrical properties, dimensional stability, transparency, chemical resistance and the like. Particularly in recent years, there has been an increase in demand for various films for optics including antireflection materials for a flat panel display and display materials associated with a touch panel. In such applications, coating processing for imparting various functions and processing for allowing the film and an electrode material or an optical film to be bonded together are frequently performed.
However, with regard to the polyester film, for example, in the transporting process, scratches are sometimes generated on the polyester film surface due to abrasion between the film and a transporting roll. Moreover, due to a heat treatment performed in the coating processing process, a polyester film as a final product has been sometimes too poor for practical use since oligomers are allowed to precipitate from the polyester film, whitening of the polyester film occurs and the surface thereof is contaminated.
On that account, various investigations have hitherto been conducted for the purpose of enhancing the hardness of a polyester film and inhibiting oligomers from precipitating. For example, an investigation for the purpose of laminating an ultraviolet-curing type acrylic resin coated film on the surface of a polyester film has been conducted (Patent Document 1). Moreover, a method of providing a coated film using a thermosetting acrylic resin and a crosslinking agent by an in-line coating method in which coating is performed within a process for the production of a thermoplastic resin film (Patent Document 2) has been studied. Moreover, there have been proposed a method of achieving the enhancement of the coated film hardness by adding a thermal initiator to an acrylic resin coated film (Patent Document 3) and a method of preventing damage by providing a coated film prepared with a binder resin and specific organic particles by off-line processing and imparting easy slipping properties (Patent Document 4).